What tests and interventions are used to diagnose and treat constipation?

Tests for Constipation

Initial Clinical Assessment

Begin with a detailed digital rectal examination that includes assessment of pelvic floor motion during simulated evacuation—this is essential before ordering any imaging or specialized testing. 1

Key Historical Elements to Elicit

• Bowel pattern specifics: Date of last defecation, frequency, stool consistency, recent changes, presence/absence of urge to defecate, sensation of complete evacuation 1, 2
• Red flag symptoms: Blood in stool, mucus, need for digital manipulation to evacuate, fecal incontinence 1, 2
• Medication review: All prescription and over-the-counter drugs, particularly opiates, anticholinergics, and calcium channel blockers 1
• Lifestyle factors: Eating/drinking habits (fiber and fluid intake), physical activity level, privacy for defecation 1, 2
• Comorbidities: Pre-existing irritable bowel syndrome, diverticular disease, heart failure, chronic pulmonary disease 1, 2

Physical Examination Components

The digital rectal examination must assess:

• Resting sphincter tone and squeeze augmentation 1
• Puborectalis muscle contraction during squeeze 1
• Perineal descent during simulated evacuation 1
• Presence of impacted feces, hemorrhoids, masses, or stenosis 1
• Patient's ability to "expel my finger" during simulated defecation 1

Abdominal examination should evaluate: Distension, masses, liver enlargement, tenderness, bowel sounds 1, 2

Perineal inspection should check for: Skin tags, fissures, prolapse, anal warts, perianal ulceration 1

Laboratory Testing

Order only a complete blood count in the absence of other symptoms—this is the single necessary test. 1, 3

Do NOT routinely order metabolic panels (glucose, calcium, thyroid-stimulating hormone) unless specific clinical features warrant them—their diagnostic utility is low and cost-effectiveness has not been proven. 1, 3

Exception: Check corrected calcium and thyroid function only if clinically suspected based on other symptoms. 1

Imaging and Structural Evaluation

When to Order Structural Imaging

Colonoscopy is indicated ONLY if:

• Alarm symptoms present: Blood in stool, anemia, weight loss 1, 3
• Abrupt onset of constipation 1, 3
• Age >50 years without previous colorectal cancer screening 1, 3

Do NOT perform colonoscopy in patients without these features. 1

Imaging Options for Structural Evaluation

First-line: Colonoscopy (provides direct visualization and biopsy capability) 3

Alternatives:

• CT colonography when colonoscopy is contraindicated 3
• Flexible sigmoidoscopy combined with barium enema 1, 3

Avoid plain abdominal radiographs for diagnosis—they have limited utility. 3

Specialized Functional Testing

When to Proceed to Functional Tests

Order these tests ONLY after:

1. Patient fails trial of fiber supplementation and over-the-counter laxatives (polyethylene glycol, milk of magnesia, bisacodyl) 1
2. Initial evaluation suggests defecatory disorder or slow-transit constipation 1

Colonic Transit Studies

Indication: Persistent symptoms despite treatment, or when anorectal tests do not show defecatory disorder 1, 3

Method: Serial abdominal radiographs after ingestion of radiopaque markers 3, 4

Anorectal Function Tests

Anorectal manometry is indicated when:

• Digital rectal examination suggests pelvic floor dysfunction (though normal exam does not exclude it) 1
• Patient reports prolonged straining, need for perineal/vaginal pressure to evacuate, or digital evacuation of stool 1

Balloon expulsion test: Useful adjunct to assess defecatory function 5

Defecography

Indication: Suspected defecatory disorders not adequately characterized by digital exam and manometry 3

Options:

• Fluoroscopic cystocolpoproctography (initial test of choice) 3
• MR defecography (provides superior soft-tissue contrast for pelvic organs and floor muscles) 3

Patient-Reported Outcome Measures

Use the Bowel Function Index (BFI) as a validated tool for assessing constipation severity, particularly for opioid-induced constipation—it is less complex than alternatives and psychometrically validated. 1, 2

Consider prescribing medication for BFI score ≥30 points with no response to initial laxatives. 1

Critical Pitfalls to Avoid

• Do NOT rely solely on digital rectal examination to exclude defecatory disorders—a normal exam does not rule them out 1
• Do NOT order excessive metabolic testing without clinical indication—this increases costs without proven benefit 1, 3
• Do NOT skip structural evaluation in high-risk patients (alarm symptoms, age >50 without screening, abrupt onset) 1, 3
• Do NOT proceed to specialized testing before attempting empiric fiber/laxative trial 1
• Recognize that plain abdominal X-rays correlate poorly with clinical assessment—one study showed no concordant correlation between physician clinical assessment scores and radiological scores 1